Field
The present specification generally relates to drilling fluids for use in petroleum engineering and drilling methods incorporating the drilling fluids and, more specifically, to rheology modifiers for drilling fluids and associated drilling methods.
Abbreviations
Å=Angstrom
ACA=1-adamantane carboxylic acid
AC=adamantane carboxylate
AHR=after hot rolling
° C.=Degrees Celsius
cm=centimeter (10−2 meter)
cm−1=wavenumber
cP=centipoise
BHR=before hot rolling
EDX=Energy-Dispersive X-Ray
ES=electrical stability
° F.=Degrees Fahrenheit
FL=fluid loss
FWHM=full width at half maximum
g=gram
h=hours
HRTEM=High-Resolution Transmission Electron Microscopy
IR=Infrared
lbf/100 ft2=pounds force per hundred square feet (1 lbf/100 ft2=0.4788 Pa)
LDH=layered double hydroxide
μm=micrometer (10−6 meter)
mL=milliliter (10−3 liter)
MPa=megapascal (106 Pascal)
nm=nanometer (10−9 meter)
OBM=oil-based mud
Pa=Pascal
psi=pounds per square inch
PV=plastic viscosity
PXRD=Powder X-ray diffraction
rpm=revolutions per minute
s=second
SEM=Scanning electron microscopy
SG=specific gravity
TEM=Transmission electron microscopy
TGA=Thermogravimetric analysis
TMO=Transition metal oxide
V=volts
YP=yield point
wt. %=weight percent
Technical Background
Drilling fluids or drilling muds are compositions that are circulated through a wellbore to facilitate drilling operations while the wellbore is being drilled. In general, drilling fluids may facilitate the removal of drill cuttings from the wellbore, may cool and lubricate the drill bit, may aid in support of the drill pipe and drill bit, or may provide a hydrostatic head to maintain the integrity of the wellbore walls and prevent well blowouts. Specific drilling fluid systems are selected to optimize a drilling operation in accordance with the characteristics of a particular geological formation. For the drilling fluid or drilling mud to perform its functions, its optimum chemical and rheological properties must be controlled.
Oil-based muds (OBMs) used in drilling typically include: a base oil (or synthetic fluid) which make up a continuous phase of an emulsion; a aqueous solution such as a saline/water solution that makes up the discontinuous phase of the emulsion; optional emulsifiers; and other optional agents or additives for suspension, weight or density, oil-wetting, fluid loss or filtration control, and rheology modifiers. The rheology modifiers commonly include organophilic clays or organophilic lignites. An oil-based drilling fluid may commonly contain from about 50:50 to about 95:5 by volume continuous phase to discontinuous phase.
Drilling in deep wells is complicated by geological conditions that involve high pressures and high temperatures (HPHT). The industry-defined definition of HPHT conditions typically include a wellbore temperature greater than 300° F. (149° C.) and a wellbore pressure greater than 10,000 psi (68.9 MPa). Known drilling fluids typically contain clay-based rheology modifiers that are not suitable for HPHT drilling because they decompose under HPHT conditions. Thus, there are ongoing needs for drilling fluids and rheology modifiers for drilling fluids that are thermally stable under HPHT conditions and that have suitable rheological properties.